The present invention relates to a measuring apparatus for supplying material to a powder molding machine for molding articles, for example, firebricks.
Apparatuses for supplying powder material to such a molding machine are mainly classified into one of two types, that is, a weight measuring type and a volume measuring or "cutting-out" type.
One such weight measuring type apparatus for supplying powder to a molding machine comprising a measuring device 12 having at least one load cell 12a (shown in FIG. 9) is mainly used in conjunction with a pressing machine using a so-called "die movement truck system", in which a die 5 is moved by a truck.
The volume measuring type supplying apparatus for a molding machine comprises in part, as shown in FIG. 10, a conveyer 11a, a hopper 11, a material inputting device 7A, and a cylinder 10. The supplying apparatus is applied to a pressing machine using a so-called "die floating type central molding system", in which the die 5 is elevated by a floating cylinder 16 as in FIG. 1.
Any conclusions about superiority or inferiority of the weight measuring type and the volume measuring or cutting-out type have not been obtained yet, at the present stage. This is because both types have merits and demerits, respectively. Also, molding conditions largely fluctuate depending on grain size and/or composition of powder material, kind of binder, etc which means that the effects of the type of supplying apparatus are masked.
With respect to the above-mentioned concepts, the applicant has already proposed a volume measuring type apparatus for supplying material in which the possibility of occurrence of material segregation (massive forming phenomenon) can be reduced for any material and measuring errors can be also reduced.
However, in recent years, error conditions (tolerance levels) are very severe and/or critical. For instance, in the case of a brick having a weight of 5 kg., an error (tolerance limit) of the dimension in the thickness direction must be within a range of .+-.0.2 mm and its value must be measured on the basis of the condition in which a material is most densely filled. In the conventional technique, change of firebrick weight upon firing is more than 20 g. Therefore, it is very difficult to fulfill such severe and/or critical conditions required in molding firebricks.
In the case of the volume measuring type apparatus, even if the accuracy is raised, there is a limitation, that is, the thickness of brick is set so as to lie within a range of .+-.0.5 to 1%. In other words, in the case of a brick weight of 5 kg., the tolerance of the thickness dimension is set so is to lie within a range from 0.5 to 1 mm. In addition, the above-mentioned conditions must be fulfilled in a state that the material is most densely filled. Therefore, in a case that only a volume measuring type supplying apparatus is used, the above-mentioned severe and/or critical conditions and tolerance levels cannot be fulfilled. In other words, a weight measuring type supplying apparatus is needed in such a case.
In the case of forming a relatively small brick, from a viewpoint of the productivity, the small brick must be molded efficiently. For this purpose, even if the measuring device 12 comprising the load cell 12a shown in FIG. 9 is applied to a volume type charger attached to, for example, the central molding pressing machine, a distance L (refer to FIG. 1) between the pressing devices, that is, an idle stroke needs to be largely increased. Also, stirring blade devices, which are provided as a countermeasure for the segregation or the like, are necessary. It is very difficult to attach those devices to the pressing machine which does not comprise such the devices.
In consideration of the above-mentioned circumstances, techniques conventionally have been demanded such that measuring errors in weight can be reduced to be as small as possible by using a load cell, segregation can be prevented, a drop height between an outlet of material supply means and a die can be reduced to as small a distance as possible, a movement surface which comes in contact with the material can be reduced to be as small as possible (since a hard material such as a grinding material or the like is frequently used as such the material), an amount of drop-out of the material can be minimized, and a tapered surface can be preliminarily formed to an surface of the supplied material (because a molded brick generally has a tapered surface). In order to improve productivity, it is desirable to utilize a pressing machine of a so-called "die floating central molding" type.